The Lempor ejector is a steam locomotive exhaust system developed by noted Argentine locomotive engineer Livio Dante Porta. The ejector's name is a portmanteau of the names of Porta and Belgian locomotive engineer Maurice Lemaître. The Lempor ejector follows the principles of the de Laval nozzle.

In steam locomotives, draft is produced in the firebox by exhausting waste steam from the cylinders into the chimney via a nozzle or 'blast pipe' to create a vacuum in the smokebox. The Lempor ejector is a development of similar multiple orifice/nozzle ejectors which create either a stronger vacuum or the same vacuum more efficiently by having less 'back pressure' or resistance to the exhausting cylinder.

The Lempor exhaust is claimed to deliver a 100% improvement in draughting capacity over traditional exhaust systems and a 40% increase in ejector performance.^{[citation needed]}